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Charger police 120mph or bust

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power loss
978 views 2 replies 2 participants last post by  ThinBlueLineCharger 
#1 ·
Ok to start out I feel it necessary to let you know that this is actually for my friends 2013 police auctioned Charger. He likes buying these cars at auction. Sometimes you win other times not so much. His most recent was a police charger that is actually not the police model but an RT. On his way across country with this new purchase he decided to let her rip. He reaches 120mph when all of the sudden it lost a few hp. It still drives normal just seems weak. No engine codes are showing up however he revels it for me and it sounded like a rc car. It no longer sounded like a reved hemi but rather my wife’s old Honda Civic. Someone told me there’s some sort of valve in the plastic manifold that may have gotten stuck causing the whine of a 4cyl and low hp but I’m not so convinced. Any help would be fantastic.
 
#2 ·
There's no valves in the intake manifold ... it's just a molded composite shell (5.7L R/T). The 6.4L SRT intake manifold has a dual shaft Short Runner Valve (SRV) bolted to the rear of the intake manifold. The Dodge RAM trucks with the 5.7L also have the SRV but the SRV was not standard for the Charger R/T. It's possible your friend's R/T was modified and had a SRT intake manifold installed (a non-factory modification done by some owners). If a SRT intake manifold is installed it could be failing and not posting any codes because the 5.7L onboard diagnostics are not checking it (i.e. not standard equipment or an option for 5.7L R/T).
If you inspect the rear of the intake manifold, a stock 5.7L R/T manifold will have a Manifold Absolute Pressure (MAP) Sensor. A intake manifold with the SRV will have the MAP sensor and the SRV.
The 5.7L R/T also has Multiple Displacement System (MDS) ... which selectively deactivates cylinders 1, 4, 6 and 7 during steady speed (i.e. goes from 8-cyl mode to 4-cyl mode). The MDS solenoids are under the intake manifold.
The 5.7L R/T (starting with 2009 models) also has Variable Cam Timing (VCT). The cam phaser is oil flow controlled by a solenoid operated control valve. The valve rotates the phaser and alters the angular position (or phasing) of the camshaft relative to the timing chain and crankshaft rotation. The VCT control valve is also under the intake manifold.

Any of the above components could cause 4-cyl like symptoms but the car's onboard diagnostics will typically post error codes when something is not functioning correctly (except for the SRV). With the lack of any diagnostic trouble codes, and no SRV, I would check the intake manifold bolts to see if they are loose and causing an air leak (vacuum leak). The bolts should be torqued to 9 ft. lbs. Tighten in sequence from the middle bolts towards the outside in a crisscross pattern.
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